This invention relates to hydraulic piston and cylinder arrangements. Devices of this type are very well known and widely used in very many different applications. In many cases a simple arrangement including a single cylinder, a piston running within the cylinder and a piston rod is provided, with suitable seals at the piston and at the end of the cylinder through which the rod passes.
Such an arrangement is of course very simple but it suffers from major disadvantages in that the outer surface of the piston rod is continually wetted with the hydraulic fluid or oil. In the usual dusty or dirty environment where such cylinders operate, the dust and particles in the air can attach readily to the layer of oil on the outer surface of the piston rod and therefore collect on that surface and are transported into the cylinder on the rod. Furthermore the oil is separated from the environment only by the single seal between the end of the cylinder and the piston rod. While this seal when new and in good condition can effectively prevent the oil from escaping from the cylinder along the piston rod, as soon as it becomes contaminated with dust or other particles or in the case that it becomes damaged, the oil can immediately escape and will tend to run down the piston rod or back over the cylinder depending upon the orientation thus losing expensive fluid which must be replaced and in some cases causing dangerous and unsightly deposits of the fluid.
It is one object of the present invention, therefore, to provide an improved piston and cylinder arrangement in which the outer surface of the piston or piston rod is maintained free from the hydraulic fluid thus reducing the danger of contamination of the seals and also reducing the possibility of oil escape even in the event of damage of one of the seals.